Desulphurizing and cracking process



.May 12, 1942. ,5, B S 2,282,451

nnsuwnumzme AND CRACKING PROCESS Filed Dec. 29, 19:58

.s UP2 HEA 7-572. 1

TAR OUTLET Patented May 12, 1942 DESULPHURIZING AND CRACKING raoor-zssBenjamin '1. Brooks, Old Greenwich, Conn, assignor to Standard AlcoholCompany Application'December 29, 1938, Serial No. 248,158

4 Claims.

This invention relates to the production of superior substantiallysulphur-free gasoline in high yields from sulphur-containing heavierhydrocarbon raw materials.

In the present cracking art, feed stocks such as gas oil containing asmall amount of sulphur are generally cracked by the usual thermaldecomposition processes wherein a portion of the sulphur is liberated ashydrogen sulphide and is drawn on with the fixed gases, while some ofthe sulphur compounds present in the feed stock, for example as organicsulphur, tends to polymerize and react with other hydrocarbons,especially the'unsaturated materials, thereby increasing the amount ofcoke and tar formed. These organic sulphur compounds are also cracked tosome extent, giving volatile sulphur compounds which are exceedingly"refractive and diflicult to remove from the heavier fractions obtainedby the distillation of the cracked product. .A considerable portion ofthis type of sulphur may be removed from the rectified products bycostly methods, such as caustic treat-.

ment, doctor sweetening, sulphuric acid and the like.

One object of this invention is to remove the sulphur from the crackingfeed stock prior to the cracking operation, thereby giving asubstantially sweet cracked product and a higher yield of crackedgasoline with low accompanyv ing yields of tar and coke. Another objectis-to provide. for a mild cracking operation prior to the main crackingstep to produce antiknock gasoline from the less refractory hydrocarbonsand to remove them from the feed stock to the cracking unit so as toprevent over-cracking. Another object is to substantially eliminate theproduction of hydrogen sulphide in the main cracking unit so as toprevent recombination of the hydrogen sulphide with the unsaturatedproducts, thereby producing sulphur compounds which must necessarily befurther removed after separation of the cracked product. Further objectswill become apparent as the description proceeds.

The present invention involves the use of three steps, i. e. adesulphurization step which may or may not be carried out under mildcracking conditions, a separation step wherein the hydrogen sulphideproduced by the desulphurization operation is removed possibly togetherwith some cracked hydrocarbons, if they are formed, from the main bodyof the uncraked oil to be fed to the third step which is the crackingunit.

It is essential that the first desulphurization step be carried out inthe presence of hydrogen and at a pressure of about 5-50 atmospheres,using a temperature of about 250-350 C. It is also desirable that ametal sulphide hydrogenating catalyst be present, such as the sulphidesof molybdenum, tungsten, chromium or uranium. If the feed stock employedis fairly low in sulphur (i. e. about 0.14%), it is desirable to carryout p MozS3+= 2MoSz+3HzS In the above example if the M0283 is completelyreduced to MOSz, the catalyst becomes inacti-' vated. Hence, it isessential that some M0283 be present during the desulphurizationoperation.

With feed stocks containing'higher amounts of sulphur, say above about1%, it is desirable to carry out this desulphurization operation withoutsubstantial cracking of the hydrocarbons. In this case the hydrogensulphide produced is withdrawn from the product in a separating vessel,since it is desirable that the desulphurization operation be carried outin the liquid phase.

After the removal of the hydrogen sulphide and possibly crackedhydrocarbons from the desulphurization unit, the desulphurized oil isfed into a cracking unit which may be of the; conventional thermalcracking type, such as the Dubbs, tube and tank, Gyro, true vapor phase,and the like, or a catalytic cracking process which employs activatedbentonites, synthetic gels and other masses as catalysts for thecracking operation.

Referring to the accompanying drawing which presents one embodiment ofthe present invention in diagrammatic sectional elevation, numeral Idenotes the introduction of a sulphurcontainingfresh feed such asreduced crude pumped into fractionating tower 2 into which enters a hotcracked product 3. In this fractionating tower tar or, other heavyproduct may be drawn oil at 5, while the main portion of the chamber byline il,'if desired. The sulphur-con -taining gases and other lightermaterials are drawn oil through vent I 2, while the remaining liquidmaterial is removed from separator Iii through line I! and forced intosuper-heating aasaaei coil l4 by pump l1 wherein the hydrocarbon rawmaterials are heated up to cracking temperature. Thence the material isforced into the cracking unit I! which may be a coil or chambercontaining catalyst, the unit being operated for optimum gasolineconversion. After the cracking operation, the cracked product iswithdrawin into the bubble tower or fractionating tower 2, wherein thegasoline recovery takes place. Although the desulphurizing chamber I maybe operated at the same pressure as the cracking unit, it is desirableto maintain a pressure of about 5-50 at mospheres in this particularvessel. It is also possible to employ a cracking coil which is merely anextension of superheater I, if desired. Provision may likewise be madefor inserting a vessel in line 3 for removing tar prior to thedistillation operation. a I

The invention may be moreclearly understood from the following examplesby which it is not intended to limit the invention in any particularrespect:

presence of an activated clay such as "Super- Filtrol, the time ofcracking being adjusted so that about 40% of the feed stock to this unitis converted into gasoline. The gasoline produced is especially. low insulphur and the amount of coke produced on the catalyst is fairly low.

By the present method it has been found pos sible to remove more of thesulphur from the feed stock than is possible by a straight crackingoperation. Furthermore, the preliminary desulphurization operation actsas a means for *preheating the feed stock for the subsequent crackingoperation so that there is no substantial loss of heat throughout all ofthe operations. If the hydrogen sulphide is not removed after thedesulphurization step and prior to the cracking operation, it tends tocombine with the unsaturates produced by the final cracking operation,giving sulphur-containing products which must then subsequently beremoved. Furthermore, by eliminating subsequent treatment of the crackedproducts to a great extent, high fed into the system in the proportionof one mole of hydrogen to five moles of feed stock. The

products issuing from this desulphurizing unit are led under pressureinto a small fractionatin g tower wherein the fixed gases containinghydrogen sulphide, hydrogen and small amounts of hydrocarbons are ledoff the top and the hydrogen is recovered for further reuse. The liquidremoved from the bottom of the tower is then fed into a tube and tankcracking unit wherein the "stock is cracked under ordinary crackingconditions for the maximum yield of gasoline, giving a stable, lowsulphur gasoline in high yields.

Example 2.A reduced crude containing 0.8% sulphur is passed into aheated tower containing chromium sulphide and alumina, together withhydrogen in the proportion of one mole of hydrogen to one mole ofoil,the temperature being 360 C. The time of contact is adjusted so thatabout 2-5 of the feed stock is converted into gasoline. The reactionmixture is then led into a distillation tower wherein the fixed gasesand gasoline are removed, the gasoline, hydrogen and hydrogen sulphidebeing separated by subsequent operations, and at least a portion of thehydrogen-hydrogen sulphide mixture is recirculated back to thedesulphurizing unit. The liquid removed from the fractionating tower isthen led into a heated vessel at atmospheric pressure and at about 565C., in

yields of gasoline are possible with minimum production of coke and tar.The amount of hydrogen which may be employed with the feed stock to thedesulphurizing unit may vary from one mole of hydrogen to twenty molesof oil, to one mole of hydrogen to one-half mole of oil, depending uponthe amount of sulphur present in the feed stock, the pressure employed,and other conditions of operation in the desulphurizing unit.

This invention is not limited to any specific examples or to any theoryof operation, but merely by the following claims in which it is intendedto cover the invention as broadly as the prior art permits.

' I claim:

1. A process for making cracked gasoline which-comprises subjecting afeed stock of relatively heavy hydrocarbons containing about .1 toabout1% sulphur to mild cracking conditions at a temperature of about 360 C.and in the presence of hydrogen, hydrogenating catalyst and addedhydrogen sulphide to remove sulphur from the feed stock and to produceabout 2% to 5% of gasoline, thereafter removing hydrogen sulphide,hydrogen and gasoline from the product, and then subjecting theremainder of the product to more severe cracking conditions thanemployed in the first cracking operation to produce the maximum yield ofgasoline.

2. The process of making an anti-knock gasoline from a gas oil ofsulphur content about .1 to about 1% which comprises subjecting said gasoil to mild cracking conditions at a temperature of about 360 C. and inthe presence of hydrogen, added hydrogen sulphide and a hydrogenatingcatalyst to remove sulphurfrom the feed stock and to produce from about2% to 5% of gasoline, thereafter removing hydrogen sulphide, hydrogenand cracked gasoline from the product and then subjecting the remainderof the product to catalytic cracking and in the presence of a crackingcatalyst to produce about 40% of gasoline on the feed to the secondcracking step. a

3. .A process for making gasoline which comprises mixing a crude oilwith cracked products leaving a cracking zone to heat the crude oil andremove volatile constituents therefrom and to provide a heated fractioncomprising relatively heavy hydrocarbons and containing from about ,1 to1% of sulphur, passing the heated fraction to a desulphurizing zonewithout further heating it and subjecting it to mild cracking conditionsat a temperature of about 360 C. in the presence oi -hydrogen, hydrogensulphide and a metal sulphide catalyst to form a relatively small amountof gasoline and to form hydrogen sulphide from the sulphur in the oil,thereafter removing hydrogen, hydrogen sulphide and gasoline from thecracked products, then subjecting the remaining hydrocarbons to moresevere 10

